1. Field of the Invention
This invention relates generally to a process for obtaining protein isolates from sunflower and colza.
2. Description of the Prior Art
New sources of protein are now being sought, owing both to the extensive malnutrition existing in more than half the world population, and also owing to the elevation of feeding habits in the industrialized countries.
Many new sources of proteins have been studied in recent years, and particularly proteins derived from plants, such as seaweeds, bacteria, yeasts, and oleaginous seeds. Notably sunflower, colza and cotton are considered to be excellent sources of protein, both because they are in abundant supply, and, except for cotton, have relatively little other commercial value.
Processes are already known for obtaining proteins from sunflowers. For instance, one such process known as the precipitation-washing technique, is described by Gheyasuddin, Cater and Mattil in Food Technology 24-242 (1970), but, of course, other similar processes are known.
In general, these prior art processes comprise the following essential steps:
A. ALKALINE SOLUBILIZATION OF THE PROTEIN CONTAINED IN THE SUNFLOWER MEAL WITH A SODIUM HYDROXIDE SOLUTION CONTAINING SODIUM SULPHITE;
B. CLARIFICATION OF THE SUSPENSION SO OBTAINED BY CENTRIFUGATION OR DECANTATION, THUS PERMITTING THE ALKALINE PROTEIN SOLUTION TO BE SEPARATED FROM THE SOLID RESIDUE WHICH IS ESSENTIALLY COMPRISED OF CELLULOSE AND HEMICELLULOSE
C. PRECIPITATION OF THE PROTEIN CONTAINED IN THE ALKALINE SOLUTION BY ACIDIFICATION AT THE ISOELECTRIC POINT, I.E. THAT POINT CORRESPONDING TO THE PH at which solubilization of the sunflower proteins is minimal and
D. PURIFICATION OF THE PROTEIN IN AN INSOLUBLE FORM OBTAINED IN THE PRECEDING STEP BY WASHING WITH WATER, FOLLOWED BY CENTRIFUGATION OR FILTRATION, THEN WASHING WITH ALCOHOL AND ETHER
The isolated proteins are dried, often by freeze-drying or spray-drying, and recovered.
These processes do not require complex apparatus, but, on the other hand do necessitate the use of large amounts of water and solvents. This implies the potential for substantial pollution problems for any firm using this process. Furthermore, some significant amounts of sunflower protein will invariably be lost in the washing water, or precipitate, obtained in step (c) due to the high solubility of some of the proteins at the process pH. Another difficulty with those processes is that they require substantial purification procedures and even then, the obtained isolates are dark colored and have been shown to be unsuited for extrusion due to the presence of mucilaginous substances which, in concentrated alkaline solutions, tend to block the extrusion nozzles.
It would be desirable therefor to provide a process whereby proteins can be isolated from such vegetative sources, whereby the isolated proteins can be provided in a purified and concentrated form, without the use of large amounts of solvents which can pose potential environmental pollution difficulties.
Protein extraction methods are also known which make use of reverse osmosis or ultrafiltration techniques.
Thus, the O' Connor reference U.S. Pat. No. 3,622,556 refers to the isolation of protein from sunflower meal, whereby the vegetable product obtained from sunflower seeds is alkali extracted, the phases separated from the extraction and the alkaline phase subjected to ultrafiltration through a semipermeable membrane having a pore diameter in the range of 10 to 80 A under a pressure ranging from 0.7 to 7 kg/cm.sup.2.
The process is effected in an inert atmosphere. Following ultrafiltration, the retentate is recovered. It was found that the recovered protein is essentially free of those substances which are likely to impart an undesirable color.
One disadvantage of that process, however, is that it requires a substantial portion of the procedure to be carried out in an inert atmosphere during extraction and separation of the phases. Moreover, O'Connor is incapable of obtaining protein isolates having at once a high dry matter content, a high nitrogenous matter content and a very low level of impurities.
As a matter of fact the removing of coloured impurities in protein fractions extracted from sunflower and colza raises difficult problems, which do not set with the same acuteness in the case of soya.